A fiber-optic amplifier of this type is known from the print publication "ECOC '89", Fifteenth European Conference on Optical Communication, Sep. 10-14, 1989, Gothenburg, Sweden, Proceedings, Vol. 1, Regular Papers TuA 5-7, pages 86-89. In this amplifier, the light radiated by a pump source and the light arriving from the signal light of the transmission line are combined in a pump coupler and are jointly transferred to an active length of fiber. However, the active length of fiber usually shows mode field diameters different from those of the pump coupler and the standardized optical waveguides of the incoming and outgoing transmission lines. For this reason, attenuation losses arise at the splices between the different optical waveguides, for both the pump light and the signal light.